Engine Drops Revs / Cuts Out

[Shel_B]

2011 Camry 4 Cylinder (2AR-FE) with 80K Miles

I frequently visit a friend who lives in the hills above my house. I often leave her place late in the evening when the temps are mid- to high-40s. I pull out of her driveway and head down the hill with the car in 1st gear. I'll get about 1/4 of the way down the hill and the engine revs drop, maybe the engine cuts out for a fraction of a second, and then jumps up to the normal revs and the car behaves normally for the balance of the drive home.

What might be causing this drop in revs? It's always about the same place on the hill, i.e., about the same length of time running.

 

[Lubener]

I would check for codes and also monitor fuel pressure as the engine is running normally, then sputters to an eventual stall. My guess is there is an issue with fuel pressure.

 

[skyactiv]

Maybe the fuel pickup is momentarily sucking air instead of fuel. How much fuel is in your gas tank when this happens?
However, you could have a pinhole leak in your fuel system that causes this only when your car is at a certain angle during the right conditions.
Vehicles age in years, too. The fuel line system and some other components of the fuel system ages faster on older vehicles that see less miles believe it or not.

 

[Shel_B]

Maybe the fuel pickup is momentarily sucking air instead of fuel. How much fuel is in your gas tank when this happens?

Always more than half a tank.

I would check for codes and also monitor fuel pressure as the engine is running normally, then sputters to an eventual stall. My guess is there is an issue with fuel pressure.

Engine neither sputters nor stalls. The revs drop and instantaneously resume. It happens so quickly that I cannot be 100% sure the engine doesn't cut out, although the tach does show about 1000rpm for a fraction of a second before jumping back to about 2000 rpm.

I should mention that when I'm going down the hill, there's no application of throttle as I'm using engine braking to maintain a low speed.

 

[Trav]

A scan tool with live date would be helpful, I suspect a sensor flaking out momentarily. Any codes?
I have seen this before, no codes, car runs normally then cat out momentarily then kick back in like nothing happened.
Crank sensors that are failing (not failed) internally commonly act this way. Not saying load the parts cannon, check it.

 

[supton]

Cold engine? My '11 has a bog of some sort around 3k. I had forgotten all about that, I think I noticed it several years ago, until I took it out the other day. But once warm it doesn't seem to do that. No idea if it would do it at other rpm's, or if whatever the cause is might be vehicle dependent.

 

[mk378]

When you're rolling downhill in gear the engine is already "cut out". The computer cuts the fuel injectors to zero if the gas pedal is not pressed and the rpm is above idle.

Which is an interesting point, after a cold start the idle speed is increased until it warms up. You may be going through the transition where fuel is injected at 1500 rpm to satisfy that, and then it is not.

I doubt the manufacturer tested the software much under these conditions. I had an old Honda that would actually stall at the stop sign at the bottom of the hill every time. There was nothing broken about it, that is just how the software worked.

 

[Shel_B]

When you're rolling downhill in gear the engine is already "cut out". The computer cuts the fuel injectors to zero if the gas pedal is not pressed and the rpm is above idle.

Which is an interesting point, after a cold start the idle speed is increased until it warms up. You may be going through the transition where fuel is injected at 1500 rpm to satisfy that, and then it is not.

I doubt the manufacturer tested the software much under these conditions. I had an old Honda that would actually stall at the stop sign at the bottom of the hill every time. There was nothing broken about it, that is just how the software worked.

I believe your assessment has some merit. As I mentioned in another response on the Toyota forum where the poster said "Possibly just an unlucky combination of the grade and the tuning for the deceleration fuel cutoff and warmup routine."

I encountered something somewhat similar to this in another situation about five - six months ago and learned that that was normal behavior. While this situation is different, it seems that there are enough similarities to give [the] suggestion credence, and is at least a good place to start looking into the behavior. Thanks!

I'm noticing that the rev range at which this happens is similar to the warm-up range switchover point. So, I think you're on to something.

I'll discuss this with my favorite tech on Monday. While it's possible that it could be something else, there's too much information now pointing in this direction to ignore the possibility. All this computer control can sometimes make things a bit complex. In the old days, the car would just blow up and you'd get a new one

 

[Rhymingmechanic]

Maybe you could test the theory by letting the car warm up a bit before starting off next time.

 

[Shel_B]

Maybe you could test the theory by letting the car warm up a bit before starting off next time.

Thanks ... returned from a 50 mile freeway drive this evening, dropped my friend off, and then headed down the hill with a fully warmed engine in 1st gear, no throttle. No dropping revs ... engine smooth the entire trip down the hill. I guess that at least partially answers the question.

Thanks to everyone for their help and suggestions.